The process of cementing textile materials together with a heat-seal adhesive is known. Thermoplastic heat-seal adhesives are applied to textiles by, for example, wiping-on powdered adhesives or thickened pastes or solutions of the adhesive, or by sprinkling-on pourable adhesive powders. It is also known to spray on the heat-seal adhesives in the form of dispersions or solutions, or to apply the adhesive in the form of filaments of fabric-web materials. The textile materials are subsequently bonded together by hot ironing. The cemented bond between the two textiles produced by the heat-sealing process should be resistant to chemical cleaners and washing.
Thermoplastics suitable for use as adhesives are primarily the polyethylenes, polyvinylchlorides and polyamides.
The use of high-pressure polyethylene as a heat-seal adhesive is disadvantageous because its resistance to chemical cleaners is inadequate. High pressure polyethylene adhesives generally cannot withstand cleaning with solvents such as perchloroethylene, since high pressure polyethylene adhesives are soluble in perchloroethylene and may swell when contacted with perchloroethylene. Although low pressure polyethylenes are resistant to cleaning, disadvantageously, they require the maintenance of severe setting conditions. The requirement of severe setting conditions limits the utility of these adhesives, and renders them unsuitable for use on sensitive fabrics, such as those described below.
Polyvinylchloride is also not optimally suited for use as a heat-seal adhesive. For plasticizing polyvinylchloride, very large quantities of plasticizers are required, i.e., about 100% based on the polyvinylchloride content, which can lead to plasticizer migration with all its associated disadvantages--namely, a decline in adhesive strength, embrittlement, etc. Also, polyvinylchloride plastisoles require setting conditions which are no longer employed by the art.
Polyamides have been widely accepted as adhesive compounds. However, due to their "hardness" they can only be considered suitable with qualification.
Polyurethane heat-seal adhesives are also known. The polyurethanes commercially available for this type of application, however, have substantial disadvantages. That is, a melting point and softening point which is too high for customary ironing temperatures and/or insufficient adhesion, and/or excessive hardness. Thus, there is no clear advantage associated with the use of known polyurethane adhesives over the polyethylene and polyamide adhesives discussed above.
Recently, thinner and more sensitive fabrics have appeared on the market, which cannot be adequately bonded with any of the above-discussed heat-seal adhesives. Raincoat fabrics, such as fine poplin fabrics, which are completely coated with a layer of polyurethane are particularly difficult to treat. If polyethylenes are used as heat-seal adhesives for these fabrics, the bond provided is minimal and inadequate. It has been found that high-pressure, as well as low-pressure, polyethylenes are unsuitable. Polyamides of various compositions likewise provide extremely little adhesion. Mixed polyvinylchloride and polyvinylacetate polymers require large amounts of plasticizer and, even then, exhibit little adhesive strength when applied to polyurethane-coated fabrics.